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DESCRIPTION:"Precision Measurements and Control of Single Molecules in Free
Solution"\n\nBy looking at molecules as individuals\, single-molecule exp
eriments can provide rich details that complement and deepen our understan
ding from bulk measurements. The ultimate goal of most single-molecule tec
hniques is to reveal population-level or time-dependent heterogeneity in a
system of interest by directly monitoring individual particles in a near-
native environment. However\, confining a single molecule within an observ
ation volume for long enough to detect a small\, noisy signal &ndash\; wit
hout substantially perturbing that signal &ndash\; is challenging\, especi
ally in situations where tethering particles in place may restrict through
put or directly change the sample&rsquo\;s behavior. Since nearly all mole
cules possess some native charge\, electrophoretic forces that are generat
ed by application of electric fields are an attractive option for manipula
ting particles without physical attachment. Similarly\, the electric field
-induced motion of ions in the double layer near the walls of a micro- or
nanofluidic channel can induce electroosmotic flow\, which imparts hydrody
namic forces that can be used to manipulate particles.\nHere\, I will pres
ent an overview of my recent work related to two unique single-molecule te
chniques that employ electric fields to enable control and precision measu
rements of single molecules and nanoscale particles in free solution. Thes
e strategies enable concurrent multi-parametric readout of the states of t
hose objects\, which then can be used to classify their nature and behavio
rs. First\, I will discuss the use of static electric fields to draw charg
ed biopolymers to and through small solid-state nanopores\, which can be u
sed to resistively sense variations in chemical or geometric structure alo
ng the length of the analyte molecule. Second\, I will present results obt
ained via an Anti-Brownian Electrokinetic (ABEL) trap\, a technique in whi
ch Brownian motion is directly counteracted by active electrophoretic or e
lectroosmotic feedback to maintain the position of a single molecule withi
n a small confocal region. Because single molecules can be trapped for man
y seconds each\, high-precision fluorescence measurements can report on ei
ther static or dynamic heterogeneity in their structure and interactions.
\nBecause these techniques utilize electrophoretic and electroosmotic forc
es\, the native charge of the analyte or surrounding medium are sufficient
to achieve tether-free nanoscale confinement of single molecules and nano
particles\, providing highly versatile sensing platforms to address both a
pplied and basic biochemical\, biophysical\, and biomedical challenges.\n\
n1-15 Squires
DTEND:20190115T220000Z
DTSTAMP:20190121T215156Z
DTSTART:20190115T210000Z
LOCATION:
SEQUENCE:0
SUMMARY:Colloquium: Dr. Allison H. Squires\, Stanford University
UID:RFCALITEM636836827161895604
X-ALT-DESC;FMTTYPE=text/html:

"Precision Measu
rements and Control of Single Molecules in Free Solution"\n\nB
y looking at molecules as individuals\, single-molecule experiments can pr
ovide rich details that complement and deepen our understanding from bulk
measurements. The ultimate goal of most single-molecule techniques is to r
eveal population-level or time-dependent heterogeneity in a system of inte
rest by directly monitoring individual particles in a near-native environm
ent. However\, confining a single molecule within an observation volume fo
r long enough to detect a small\, noisy signal &ndash\; without substantia
lly perturbing that signal &ndash\; is challenging\, especially in situati
ons where tethering particles in place may restrict throughput or directly
change the sample&rsquo\;s behavior. Since nearly all molecules possess s
ome native charge\, electrophoretic forces that are generated by applicati
on of electric fields are an attractive option for manipulating particles
without physical attachment. Similarly\, the electric field-induced motion
of ions in the double layer near the walls of a micro- or nanofluidic cha
nnel can induce electroosmotic flow\, which imparts hydrodynamic forces th
at can be used to manipulate particles.

\n

Here\, I will present an o
verview of my recent work related to two unique single-molecule techniques
that employ electric fields to enable control and precision measurements
of single molecules and nanoscale particles in free solution. These strate
gies enable concurrent multi-parametric readout of the states of those obj
ects\, which then can be used to classify their nature and behaviors. Firs
t\, I will discuss the use of static electric fields to draw charged biopo
lymers to and through small solid-state nanopores\, which can be used to r
esistively sense variations in chemical or geometric structure along the l
ength of the analyte molecule. Second\, I will present results obtained vi
a an Anti-Brownian Electrokinetic (ABEL) trap\, a technique in which Brown
ian motion is directly counteracted by active electrophoretic or electroos
motic feedback to maintain the position of a single molecule within a smal
l confocal region. Because single molecules can be trapped for many second
s each\, high-precision fluorescence measurements can report on either sta
tic or dynamic heterogeneity in their structure and interactions.

\n

Because these techniques utilize electrophoretic and electroosmotic force
s\, the native charge of the analyte or surrounding medium are sufficient
to achieve tether-free nanoscale confinement of single molecules and nanop
articles\, providing highly versatile sensing platforms to address both ap
plied and basic biochemical\, biophysical\, and biomedical challenges.\n\n1-15 Squi
res